Non-invasive reading of bio-electric signals from the body is inherently challenging because the signals are often weak and much of the information is often at low frequencies. As a result, high-gain and low-noise amplifiers are required. However, traditional capacitive DC blocking cannot be used between amplifier stages because the series capacitors block substantial low-frequency information unless the series capacitors are prohibitively large.
Furthermore, for ultra-low power applications, the power consumption required for high gain amplifiers can be prohibitively large. The reading of bio-electric signals is even more challenging in large-area and flexible electronics because thin-film transistors (TFTs) have lower performance than VLSI transistors and complementary (e.g., both n-channel and p-channel) TFTs are typically not available or feasible.
A need therefore exists for improved amplifiers for capacitive reading of low-amplitude and low-frequency signals.